Attenuator methods



M. DOLIN ET Al.

March 14, 1961 ATTENUATOR METHODS 2 Sheets-Sheet 1 Original Filed Nov. 15, 1954 March 14, 1961 M. DOLIN ETAL ATTENUATOR METHODS 2 Sheets-Sheet 2 Original Filed Nov. 15, 1954 BY IVICHOLIS M PQUI I 45 I a A. r ATTO United States Patent ATTENUATOR METHODS Martin Dolin, Glen Oaks, Aldo M. Scandurra, New

York, and Nicholas M. Poulos, Great Neck, N.Y., assignors to Applied Research Inc., Flushing, N.Y., a corporation of New York Original application Nov. 15, 1954, Ser. No. 468,818. Divided and this application Dec. 16, 1958, Ser. No. 788,250

1 Claim. (Cl. 29-155.63)

This invention relates to attenuators for electric circuits and more specifically concerns a fixed pad attenuator for insertion in high frequency circuits to attain a predetermined reduction in signal level.

High frequency attenuators heretofore have posed a serious problem to the electronic industry because electrical or mechanical disturbances of a transmission line may produce substantial power losses through the production of standing waves therein. Attenuators are generally connected in series with a transmission line and include various combinations of resistive and reactive components. In order to obtain satisfactory results and a reasonably low standing wave ratio, considerable effort has been made to attain a high degree of impedance stabilization and symmetry with the result that present known attenuators are relatively large, cumbersome and expensive. In addition increases in frequency further aggravates the attenuator problem particularly in coaxial transmission lines and in such cases even the smallest deviations from true symmetry will result in substantial power losses.

Accordingly one object of this invention is to provide an improved attenuator particularly useful in connection with coaxial transmission lines that will provide an exceedingly good standing wave ratio at frequencies of the order of 3,000 megacycles and even higher.

Another object of the invention is a new and improved high frequency attenuator having an improved voltage standing wave ratio and that is characterized by its simplicity, ruggedness and stability.

Still another object of the invention is to provide an attenuator that may be readily inserted in a coaxial line, that will maintain its accuracy over extended periods of time and may be arranged and designed to provide a predetermined impedance and attenuation that will be substantially uniform for frequencies up to and even exceeding 3,000 megacycles.

The above and other objects of the invention will become more apparent from the following description and accompanying drawings forming part of this application.

In the drawings:

Fig. l is an enlarged perspective view of a coaxial connector embodying an attenuator in accordance with the invention;

Fig. 2 is an exploded view of the connector shown in Fig. 1;

Fig. 3 is a crosssectional view of the embodiment shown in Fig. 1;

Figs. 4 and 5 are cross sectional views taken along the lines 4--4 and 5-5 of Fig. 3; and

Fig. 6 is a circuit diagram of the embodiment of the invention illustrated in Fig. 1.

While the embodiment of the invention now to be described has 'been illustrated in the form of a connector for coaxial high frequency transmission lines, it is apparent that certain features thereof are equally applivcable to other types of connectors such as those used .in connection with open or unshielded transmission lines.

ice

The attenuator in the illustrated embodiment of the invention is contained within a housing 10 consisting of male and female connector parts 12 and 14 respectively which are coupled one to the other to form a substantially unitary device for insertion in series with a line. The male connector portion 12 is in the form of a bayonet plug and comprises a substantially cylindrical metal body 16 having a knurled flange 18 at one end thereof and an enlarged cylindrical section 20 extending from the other side of said flanged portion 18. Within the cylindrical section 16 of the male connector is a tubular insulating member 21 having an enlarged section 2 which closely fits the internal contour of the cylindrical portion 16 and is held in place therein by at least two indents 23 which engage corresponding depressions in the enlarged section 22. Within the forward cylindrical portion 21 of the insulating member 21 is a hollow terminal member 24 having an enlarged portion 25 which cooperates with the corresponding opening in the insulator 21 to hold the terminal in alignment therein. The forward tubular portion 26 of terminal 24 is slotted to form a spring clip to receive a cooperating pin in a female connector of the type shown in the connector part 14.

The cylindrical member or sleeve 16 of the male connector part is provided with a pair of bosses or pins 27 adapted to engage corresponding grooves in a cooperating female connector to secure it in position therein.

The female connector part 14 is adapted to receive a male connector of the type illustrated at 12 and has an inner cylindrical member 30 of brass or other suitable conductive material. A sleeve 31 integrally formed with member 30 and extending forwardly thereof is provided with a plurality of longitudinal slots 32 and is of a diameter that will form a firm mechanical and electrical connection with the body of a cooperating male connector similar to the connector 12. Rearwardly of the body member 30 is an integrally formed tubular section 33 having a diameter identical to that of the tubular section 20 of the male connector part 12 as previously described.

Surrounding the body part 30 and rotatably mounted thereon is a bayonet sleeve for cooperating with and attachment to the male connector part to hold it in engagement with the female connector. This sleeve 34 is held in position on the body part 30 by an enlarged section 39 bridging a pair of Washers 35 and 35' with the washer 35 being set in a groove 36 in the housing part 30 and the washer 35' being held against a shoulder 37 by means of an intervening spring member 38. The forward edge 40 of the enlarged section 39 is held in spaced relationship to the washer 34 by a spacer of insulating material 41 and the rear edge 42 of this enlarged section 39 is rolled over the outer edge of the washer 35 to secure the entire assembly in position on the housing 30. With this arrangement the sleeve 34 can be rotated and moved forwardly against the action of spring 38 so that a firm connection with a male connector will be secured. The cylindrical part 43 of the sleeve 34 is provided with a pair of helical slots 44 to receive the pins 27 of a male connector 12 and in order to insure rigidity of the outer end thereof a flanged end 45 is provided which has a diameter greater than the outer diameter of the pins 27 so that the longitudinal portion 44 of the slots 44 will not break through the outer surface of the flanged portion 45 as may be observed in Figs. 1 and 2.

Within the body member 30 of the female connector 14 is a tubular insulating member 46 for receiving and holding the terminal 47. It is held in place within the housing 30 by two or more indents 46'. The terminal 47 has an enlarged portion 48 which is received in an opening 49 in the insulator 46 and lies against the inwill extend out through the slots 57 and 58.

Wardly extending flange 50. The tubular section 52 of the insulator 46 extends forwardly to a point spaced from the end of sleeve 34 and surrounds the elongated connector pin 51 which has a pointed end part to facilitate engagement with a terminal such as terminal 24 discussed in connection with the male connector part 12.

The internal diameter of the insulator section 52 sur rounding the pin portion 51 is slightly greater than the outside diameter of the section 21 of the insulator 21 in the male connector part 12 so that when a male connector similar to connector 12 is coupled thereto a firm mechanical and electrical connection will be secured with a substantially water tight seal therebetween.

In accordance with the invention the electrical attenuator which comprises three resistors 53, 54 and 55 is housed within a sleeve 56 of metal, plastic or the like disposed within the cylindrical. portions and 33 of the connectors 12 and 14 respectively. The resistors are arranged in parallel relationship one to the other and connected to form a pi network as shown in Fig. 6. The resistor 54 of this network is connected directly between the terminal members 24 and 47 and constitutes the series resistor of the pi network. The terminal 26 is connected through resistor 54 to the casing or shield which in the present embodiment constitutes the metallic bodies of the connectors 12 and 14 and the resistor 53 is connected between'the terminal 47 and the connector bodies. The terminal leads 53 and 55 of the resistors 53 and 55 respectively are brought out through slots 57 and 58 which are formed in the cylindrical sections 33 and '20 of the two connector parts, respectively. Thus in the assembly of the device as may be observed in Fig. 2 the resistors are coupled one to the other and to the terminals 26 and 47 as described. The metallic sleeve 56 is then slipped over the resistors and the connector parts 12 and 14 are positioned in place over the sleeve 56. This automatically positions the terminals 26 and 47 within their respective connectors and leads 53' and 55 If desired the connector parts may be soldered together whereupon the leads 53 and 55' are then soldered to the bodies of the connectors to complete the wiring. It will be observed that with the disposition of the three resistors in this way a symmetrical attenuator is provided. By properly selecting resistors having the desirable physical size capacitive reactances will be maintained at a minimum and a substantially pure resistive attenuator will be secured. If desired the leads 54' and 54" extending from the resistor 54 may be provided with a suitable insulating material to avoid any possibility of short circuits.

Although any suitable type of resistor may be employed in the attenuating network, composition carbon resistors are preferred in order to avoid inductive effects.

Such a resistor may comprise carbon granules mixed with a suitable phenolic compound and compressed or molded to form a unitary body with the connecting leads securely embedded therein.

The accuracy of an attenuator, as is well-known, is dependent upon the accuracy of the individual elements comprising itand since the impedance of an attenuator in applications of this character is important in order to obtain a good standing wave ratio it is not only important that the resistors maintain their proper values relative one to the other but should maintain a desired absolute value in order that the impedance of the network will not vary.

It has been found that by properly treating and preparing composition carbon resistors, extremely high accuracies and stability can be obtained. To this end the resistors to be embodied in a given network are selected with values somewhat below the desired computed values. The resistors are then preferably baked at about degrees ccntigrade for two separate periods of about ten to fifteen minutes each though equivalent procedures may be employed. Baking the resistors in this way has been found to stabilize them and prevent them from changing value with age. After the stabilizing process the resistors are then adjusted to the proper value by grinding away a portion of the surface to leave an intended section therein. After the desired resistance is secured, each resistor is then preferably coated with a siutable temperature and moisture resistant coating such as glyptol or other suitable plastic and then baked for a period of about ten minutes at a temperature of the order of 100 degree centigrade. The resistors are then cooled and checked to be sure that the proper resistance has been maintained. While the resistors need not be coated with an insulating compound as discussed above, such a procedure is preferred as it affords both mechanical and electrical protection.

The attenuator as described above has been found to produce standing wave ratios of less than 1.07:1 at frequencies up to and exceeding a thousand megacycles and comparatively good ratios as high as three thousand megacycles. At lower frequencies standing wave ratios of the order of 1.04:1 are readily obtainable. These attenuators have also been found to maintain their characteristics and over long periods of time with little change in the standing wave ratio and provide a sturdy dependable device that will readily Withstand severe mechanical shock and substantial changes in ambient temperature without adverse eifects on its operation.

This application is a division of our prior application for United States patent Serial No. 468,818, entitled Attenuator, filed November 15, 1954-.

While only one embodiment of the invention has been described, it is apparent that modificttions, changes and alterations may be made without departing from the true scope and spirit thereof.

What is claimed is:

The method of treating and calibrating a molded carbon resistor comprising the steps of subjecting said resister to at least two successive heating cycles with the resistor being heated to approximately 100 C. for a period of at least 10 minutes during each cycle, calibrating the resistor by removing a portion of the body thereof, coating the calibrated resistor with an insulating material and then subjecting the calibrated and coated resistor to at least one reheat cycle of approximately 100 C. for about 10 minutes.

References Cited in the file of this patent UNITED STATES PATENTS 2,159,106 Richter May 23, 1939 2,330,782 Morelock Sept. 28, 1943 2,472,801 Barfield et al. June 14, 1949 2,705,749 Daily et al. Apr. 5, 1955 

